Here's the Georgia Supreme Court decision, which is 4-3. The bottom line:

[W]e conclude that the habeas court properly ruled that Wilson’s sentence of ten years in prison for having consensual oral sex with a fifteen-year-old girl when he was only seventeen years old constitutes cruel and unusual punishment.

I'll have more when I finish reading the case. Thanks to Aeon Skoble (HNN) for the pointer.

UPDATE: As promised, here's more (some paragraph breaks added):

Legislative enactments are the clearest and best evidence of a society’s evolving standard of decency and of how contemporary society views a particular punishment. In determining whether a sentence set by the legislature is cruel and unusual, this Court has cited with approval Justice Kennedy’s concurrence in Harmelin v. Michigan. Under Justice Kennedy’s concurrence in Harmelin, as further developed in Ewing v. California, in order to determine if a sentence is grossly disproportionate, a court must first examine the "gravity of the offense compared to the harshness of the penalty" and determine whether a threshold inference of gross disproportionality is raised.

In making this determination, courts must bear in mind the primacy of the legislature in setting punishment and seek to determine whether the sentence furthers a "legitimate penological goal" considering the offense and the offender in question. If a sentence does not further a legitimate penological goal, it does not "reflect[] a rational legislative judgment, entitled to deference," and a threshold showing of disproportionality has been made. If this threshold analysis reveals an inference of gross disproportionality, a court must proceed to the second step and determine whether the initial judgment of disproportionality is confirmed by a comparison of the defendant’s sentence to sentences imposed for other crimes within the jurisdiction and for the same crime in other jurisdictions....

Here, the legislature has recently amended § 16-6-4 to substitute misdemeanor punishment for Wilson’s conduct in place of the felony punishment of a minimum of ten years in prison (with the maximum being 30 years in prison) with no possibility of probation or parole. Moreover, the legislature has relieved such teenage offenders from registering as a sex offender. It is beyond dispute that these changes represent a seismic shift in the legislature’s view of the gravity of oral sex between two willing teenage participants. Acknowledging ... that no one has a better sense of the evolving standards of decency in this State than our elected representatives, we conclude that the amendments to § 16-6-4 and § 42-1-12 [the sex offender registration statute] reflect a decision by the people of this State that the severe felony punishment and sex offender registration imposed on Wilson make no measurable contribution to acceptable goals of punishment.

[Footnote: Although the dissent correctly notes that the General Assembly stated that the 2006 Amendment to § 16-6-4 should not be applied retroactively, the dissent erroneously concludes that the cruel and unusual punishment analysis ends there.... [C]ruel and unusual punishment is an evolving constitutional standard and ... the most objective evidence of that evolving standard are legislative enactments.... Thus, although this Court cannot apply the 2006 Amendment to § 16-6-4 retroactively, we can rely on that amendment as a factor representative of the evolving standard regarding the appropriate punishment for oral sex between teenagers.]

Stated in the language of Ewing and Harmelin, our legislature compared the gravity of the offense of teenagers who engage in oral sex but are within four years of age of each other and determined that a minimum ten-year sentence is grossly disproportionate for that crime. This conclusion appears to be a recognition by our General Assembly that teenagers are engaging in oral sex in large numbers; that teenagers should not be classified among the worst offenders because they do not have the maturity to appreciate the consequences of irresponsible sexual conduct and are readily subject to peer pressure; and that teenage sexual conduct does not usually involve violence and represents a significantly more benign situation than that of adults preying on children for sex....

[B]ased on the significance of the sea change in the General Assembly’s view of the appropriate punishment for teenage oral sex, we could comfortably conclude that Wilson’s punishment, as a matter of law, is grossly disproportionate to his crime without undertaking the further comparisons outlined in Harmelin and Ewing. However, we nevertheless will undertake those comparisons to complete our analysis.

A comparison of Wilson’s sentence with sentences for other crimes in this State buttresses the threshold inference of gross disproportionality. For example, a defendant who gets in a heated argument and shoving match with someone, walks away to retrieve a weapon, returns minutes later with a gun, and intentionally shoots and kills the person may be convicted of voluntary manslaughter and sentenced to as little as one year in prison. A person who plays Russian Roulette with a loaded handgun and causes the death of another person by shooting him or her with the loaded weapon may be convicted of involuntary manslaughter and receive a sentence of as little as one year in prison and no more than ten years. A person who intentionally shoots someone with the intent to kill, but fails in his aim such that the victim survives, may be convicted of aggravated assault and receive as little as one year in prison. A person who maliciously burns a neighbor’s child in hot water, causing the child to lose use of a member of his or her body, may be convicted of aggravated battery and receive a sentence of as little as one year in prison. Finally, at the time Wilson committed his offense, a fifty-year-old man who fondled a five-year-old girl for his sexual gratification could receive as little as five years in prison, and a person who beat, choked, and forcibly raped a woman against her will could be sentenced to ten years in prison.

There can be no legitimate dispute that the foregoing crimes are far more serious and disruptive of the social order than a teenager receiving oral sex from another willing teenager. The fact that these more culpable offenders may receive a significantly smaller or similar sentence buttresses our initial judgment that Wilson’s sentence is grossly disproportionate to his crime. Finally, we compare Wilson’s sentence to sentences imposed in other states for the same conduct. A review of other jurisdictions reveals that most states either would not punish Wilson’s conduct at all or would, like Georgia now, punish it as a misdemeanor. Although some states retain a felony designation for Wilson’s conduct, we have found no state that imposes a minimum punishment of ten years in prison with no possibility of probation or parole, such as that provided for by former § 16-6-4. This review thus also reinforces our initial judgment of gross disproportionality between Wilson’s crime and his sentence.

The dissent indeed relies, as the footnote suggests, chiefly on the fact that the legislature decided that the 2006 Amendments to § 16-6-4 shouldn’t be applied retroactively. It also generally relies on the deference due legislative judgments about sentences, and on Widner v. State, a 2006 Georgia Supreme Court case that the majority distinguishes. (I won’t get into that debate; if you’re interested, read Widner and the Wilson opinions’ discussion of Widner.)

My sense of the matter: I think there are institutional problems with courts’ evaluating the length of confinement under the Cruel and Unusual Punishment Clause; it’s hard to see a good legal rule that courts can sensibly apply in a wide range of cases, and to my knowledge there isn’t the sort of textual or original meaning evidence that strongly points to requiring courts to engage in such a mushy judgment. But the Supreme Court has said that such evaluation should take place, though with a great deal of deference to the legislature. And if there is to be such an evaluation, this would look like an excellent case for setting the sentence aside, for the reasons the majority mentions.

The Georgia Legislature has decided that consensual oral sex between 17- and 15-year-olds is not a very serious transgression. (It had decided the same about genital sex years before.) That has to be the implicit judgment behind making it a misdemeanor, and the nonretroactivity provision doesn’t undermine this implicit judgment. This judgment, coupled with the comparisons with other crimes and with the behavior of other jurisdictions — and the absence of statutory aggravating factors, such as the past convictions at issue in the California Three Strikes law, which the Court has upheld — provides strong and objective evidence in favor of the Georgia Supreme Court’s conclusion.

I should say that I at first thought there was no Cruel and Unusual Punishment Clause issue here, but the Georgia Supreme Court’s analysis has persuaded me.

Finally, for those who wonder about the racial dimensions of the case, note that the four white Justices on the Georgia Supreme Court split 2-2, and the three black Justices split 2-1 in Wilson’s favor — no stark racial disparity here (though, as I noted earlier, there was "little reason to assume that there’s much of a racial dimension here" even before this decision).